This invention relates to synchronous switched vertical deflection (SSVD) for television display arrangements in which energy for generating the vertical deflection current is extracted from the horizontal deflection circuit during both the horizontal trace and retrace intervals.
U.S. Pat. No. 4,048,544 issued Sept. 13, 1977 to P. Haferl describes an SSVD system in which energy is extracted from the horizontal deflection generator during the horizontal retrace interval. In the Haferl arrangement, a first winding coupled to the horizontal deflection generator is coupled in series with a controllable switch in the form of an SCR and an inductor to charge a capacitor in a first polarity for driving current in one direction through the vertical deflection winding. A second series arrangement of an SCR, a winding and an inductor is coupled to the capacitor for charging it in a second polarity for driving current in the opposite direction through the vertical deflection winding.
The energy coupled through one of the series charging paths in an SSVD arrangement is highly sensitive to the time at which the SCR is gated into conduction. Immediately before the end of the horizontal retrace interval, the retrace pulse voltage is small, and a relatively small current flows in the path with correspondingly small energy transfer. Advancing the gating time not only increases the time during which current may increase in the charging inductor, but also increases the peak magnitude of that portion of the retrace pulse voltage applied to the charging inductor. Thus, small changes in the gating time can result in large changes in the energy coupled from the horizontal deflection generator to the vertical deflection winding. The large voltages and currents and rates of change of voltages and currents involved in the SSVD tends to cause coupling of energy from the power circuits to the control circuit. As a result, the earlier-gated SCR causes large changes in voltages and currents in the power circuit which when coupled to the control circuit by conductors and other coupling paths tends to cause early gating or "pulling" of the latergated SCR. This, in turn, may cause shading of the raster, which is known as "white line" or "black line". The shading results from changes in the velocity of the vertical scan, by which the scanned spot dwells for greater or lesser duration in particular portions of the vertical scan.
It is desirable to eliminate wound components generally and particularly desirable to eliminate windings on the flyback transformer. It is also desirable to reduce shading of the raster resulting from the tendency of the firing of one SCR pull the trigger time of the other.